CN112106312A

CN112106312A - Multi-fiber interface automatic power reduction system and method

Info

Publication number: CN112106312A
Application number: CN202080002075.7A
Authority: CN
Inventors: 切多尔·保罗
Original assignee: HILLER
Current assignee: HILLER
Priority date: 2019-03-26
Filing date: 2020-03-25
Publication date: 2020-12-18
Anticipated expiration: 2040-03-25
Also published as: CA3134004A1; US10778329B1; EP3741054A1; WO2020198294A1; CN112106312B; US20200313766A1; JP2022526049A; JP7304364B2; EP3741054B1; US10541748B1

Abstract

An optical module (10) comprising a plurality of ports (12) configured to connect to a multi-fiber cable comprising transmit and receive optical fibers for the plurality of ports (12); a detector for each of the plurality of ports, the detector configured to detect loss of signal at a port level; and a processor (24) configured to perform automatic power reduction only on affected ports of the multi-fiber cable where a loss of signal is detected. The multi-fiber cable can be an MPO cable.

Description

Multi-fiber interface automatic power reduction system and method

Technical Field

The present disclosure relates generally to the field of optical networks. More particularly, the present disclosure relates to multi-fiber interface Automatic Power Reduction (APR) systems and methods based on spectrum specific Wavelength Selective Switch (WSS) response.

Background

Automatic Power Reduction (APR) is a term used in the context of laser safety. The system fiber typically has more power than is acceptable for an open interface. Therefore, the system must detect an open connection and then reduce power for a certain amount of time to limit exposure and potential eye damage. This is specified, for example, by IEC 60825.

Colorless undirected (CD), colorless undirected add (CDA), and colorless undirected content-free (CDC) reconfigurable optical add-drop multiplexer (ROADM) architectures continue to be popular. These ROADM types typically utilize multi-fiber push on (MPO) style cables and the like to maintain manageability of the fibers within the node. Roughly speaking, these multi-fiber cables are considered to be single point sources from the perspective of laser safety. Thus, based on certain conditions, for example, the sum of the launch powers of all the sub-fibers cannot exceed the limit of about 21.3dBm at 1M ("1M") for IEC 60825. Thus, if there are four active sub-fibers per cable, the maximum value for each sub-fiber is about 15.3 dBm.

In previous ROADM designs, this limitation can be observed without any reaction mechanism. The targets of the number of channels, their spectral occupancy and the system Power Spectral Density (PSD) result in a total power below the maximum per sub-fiber required of 1M. In general, the PSD target of a channel remains unchanged regardless of its spectral occupancy. Thus, the power requirement of the clear channels Mux/demux (ccmd) is related not only to the number of channels but also to their spectral occupancy.

In conjunction with evolving technology, the drive to increase capacity has resulted in a change that effectively increases the total spectrum and correspondingly increases the power that a Wavelength Selective Switch (WSS) must direct to a given CCMD (i.e., each sub-fiber). An increase in baud rate (e.g., 56, 75, 90+ GBaud) results in higher spectral occupancy of these channels. In addition, the number of add/drop channels per CCMD is also increasing (e.g., 12 to 24 +). Also, channel pre-combining is used as a port multiplier for the number of channels per CCMD (e.g., 4x 24).

These variations collectively result in a given CCMD potentially including 96 channels, each with a frequency spectrum in excess of 90 GHz. In practice, this is already sufficient to fill many degrees of the C or L band. Thus, it is no longer possible to remain below the 1M limit for cables that do not respond proactively. A particular challenge is to avoid collateral damage to signals on other ports. Therefore, what is needed is a spectrally selective response to one or more corresponding APR triggers.

In the past, retention mechanisms or back-reflection based APR were often used to maintain the safety requirements of the laser. Due to the amount of spectrum, power is therefore routed to a given CCMD port, it is no longer possible to keep the amplifier to a power below eye safety limits. Back reflection based APRs are no longer available due to the Angled Physical Contact (APC) termination of single mode MPO cables.

Disclosure of Invention

In various exemplary embodiments, the present disclosure provides a spectrum/port specific APR system and method that relies on rapid changes in WSS liquid crystal on silicon (LCoS) or grating-like patterns based on corresponding LOSs of input signal (LOS). Thus, a spectrum-specific WSS response is utilized. It should be noted that LCoS is only an exemplary technology herein.

In one exemplary embodiment, the present disclosure provides an Automatic Power Reduction (APR) system for an optical network module, the system comprising: a multi-fiber interface comprising a plurality of ports adapted to couple to one or more multi-fiber connectors; a card processor operable to detect loss of signal on an input port of the plurality of ports and to compare power of an associated output port to an activation threshold received by the card processor; and a module processor operable to trigger the optical network module to execute an APR procedure and attenuate a spectrum associated with an affected port using a wavelength selective switch coupled to the plurality of ports if a signal loss is detected on the input port and the power of the output port exceeds an activation threshold. Alternatively, the card processor and the module processor are respective functional parts of the same processor. The module processor is further operable to refuse to trigger the optical network module to perform an APR procedure and attenuate a spectrum associated with an affected port using the wavelength selective switch coupled to the plurality of ports if a signal loss is detected on the input port but the power of the output port does not exceed the activation threshold. Triggering the optical network module to execute the APR program includes causing the optical network module to execute the APR program at a higher priority than other programs using the hardware line. Attenuating the spectrum associated with the affected port using a wavelength selective switch coupled to the plurality of ports includes attenuating the spectrum associated with the affected port by a predetermined amount received by the module processor. Alternatively, attenuating the spectrum associated with the affected port using a wavelength selective switch coupled to the plurality of ports comprises attenuating the spectrum associated with the affected port by a variable amount that is dependent on a difference between the power of the output port and an activation threshold received by the module processor.

In another exemplary embodiment, the present disclosure provides an Automatic Power Reduction (APR) method for an optical network module, the method comprising: given a multi-fiber interface comprising a plurality of ports adapted to be coupled to one or more multi-fiber connectors, detecting, at the card processor, a loss of signal on an input port of the plurality of ports and comparing power of an associated output port to an activation threshold received by the card processor; and in the event that a signal loss is detected on the input port and the power of the output port exceeds an activation threshold, triggering, at the module processor, the optical network module to perform an APR procedure and attenuate a spectrum associated with the affected port using a wavelength selective switch coupled to the plurality of ports. Alternatively, the card processor and the module processor are respective functional parts of the same processor. The method also includes, in the event that a signal loss is detected on the input port but the power of the output port does not exceed the activation threshold, denying, at the module processor, triggering the optical network module to perform an APR procedure and attenuating a spectrum associated with the affected port using a wavelength selective switch coupled to the plurality of ports. Triggering the optical network module to execute the APR program includes causing the optical network module to execute the APR program at a higher priority than other programs using the hardware line. Attenuating the spectrum associated with the affected port using a wavelength selective switch coupled to the plurality of ports includes attenuating the spectrum associated with the affected port by a predetermined amount received by the module processor. Alternatively, attenuating the spectrum associated with the affected port using a wavelength selective switch coupled to the plurality of ports comprises attenuating the spectrum associated with the affected port by a variable amount that is dependent on a difference between the power of the output port and an activation threshold received by the module processor.

In another exemplary embodiment, the present disclosure provides a computer-readable medium storing computer-executable instructions configured to cause the following steps to occur: given a multi-fiber interface comprising a plurality of ports adapted to be coupled to one or more multi-fiber connectors, detecting, at the card processor, a loss of signal on an input port of the plurality of ports and comparing power of an associated output port to an activation threshold received by the card processor; and in the event that a signal loss is detected on the input port and the power of the output port exceeds an activation threshold, triggering, at the module processor, the optical network module to perform an Automatic Power Reduction (APR) procedure and attenuate a spectrum associated with the affected port using a wavelength selective switch coupled to the plurality of ports. Alternatively, the card processor and the module processor are respective functional parts of the same processor. The steps further include, in the event that a signal loss is detected on the input port but the power of the output port does not exceed the activation threshold, denying, at the module processor, triggering the optical network module to perform an APR procedure and attenuating a spectrum associated with the affected port using a wavelength selective switch coupled to the plurality of ports. Triggering the optical network module to execute the APR program includes causing the optical network module to execute the APR program at a higher priority than other programs using the hardware line. Attenuating the spectrum associated with the affected port using a wavelength selective switch coupled to the plurality of ports includes attenuating the spectrum associated with the affected port by a predetermined amount received by the module processor. Alternatively, attenuating the spectrum associated with the affected port using a wavelength selective switch coupled to the plurality of ports comprises attenuating the spectrum associated with the affected port by a variable amount that depends on a difference between the power of the affected port and an activation threshold received by the module processor.

Drawings

The present disclosure is illustrated and described herein with reference to the various drawings, in which like reference numerals are used to refer to like system components/method steps, where appropriate, and in which:

FIG. 1 is a schematic diagram illustrating one exemplary embodiment of an APR system of the present disclosure;

FIG. 2 is a flow chart illustrating one exemplary embodiment of an APR method of the present disclosure;

fig. 3 is a schematic diagram illustrating APR applied to the spectrum of affected ports only, in accordance with the APR systems and methods of fig. 1 and 2;

FIG. 4 is a schematic diagram showing the need for each sub-fiber APR to respond so that other ports are unaffected; and

fig. 5 is a flow chart illustrating an Automatic Power Reduction (APR) process for an optical network module.

Detailed Description

Further, in general, the present disclosure provides a spectrum/port specific APR system and method that relies on rapid changes in the WSS LCoS raster pattern based on a corresponding input LOS. Thus, spectrum specific WSS responses are utilized.

A challenge with multi-fiber interfaces, such as MPO ports, is that the collection of sub-fibers is considered a single-point (or near single-point) source due to the small spacing between the sub-fibers. Thus, a 1M safety limit is used for the sum of the light emissions of all the sub-fibers. In the C-band, this limit is about 21.3dBm, which corresponds to no more than about 15.3dBm per sub-fiber in the case of four pairs of fibers per cable.

For example, in previous generations of CDC ROADMs, the power of each sub-fiber may be kept below a maximum level while still achieving the appropriate PSD needed for proper system performance. However, there are a maximum of 16 channels at 56 Gbaud. In recent CDC ROADM designs, it is no longer possible to achieve the required PSD without exceeding the limit of about 15.3dBm per sub-fiber. This is due to the large increase in total signal spectrum, the increase in supported baud rate (i.e., spectrum occupancy), and channel precombinations associated with the add/drop channel hopping 24 for each CCMD.

Table 1 shows how it is possible, but no longer possible, to stay below the 1M limit as a set in the previous generation CDC (CCMD8x16@56 GHz). The latest CCMD designs are now able to accommodate 96 channels at frequencies of 90GHz or higher. This is sufficient to fill the spectrum in two dimensions (degrees).

Table 1: comparing power requirements of each sub-fiber based on CCMD ports and signal baud rates

The present disclosure takes advantage of the properties of bidirectional optical fiber pairs in a multi-fiber cable. The transmit (demux) and receive (mux) fiber pairs for a given port are collocated in the same MPO cable. In this way, the incoming LOS can be used to detect open connections. Unlike duplex LC connectors, it is not possible to subdivide MPO cable sub-fibers, so the incoming LOS represents a reliable detection mechanism. Since the standard for single mode MPO cables is APC termination, this makes reflection-based detection impossible.

When a LOS is detected on the input port, its response is: the power of the spectrum cross-connected to the port is reduced by the attenuation capabilities of the WSS module. Thus, traffic on other ports is not affected. Before responding, additional logic compares the output power to an activation threshold. If the power on this port is already below the multi-fiber maximum, the system may choose to skip the APR response.

To meet the level 1M timing requirements, Hardware (HW) lines can be used to interrupt all other WSS module processes and prioritize the power reduction of one or more ports as needed. The following figure illustrates and describes how this mechanism can be implemented.

Referring now specifically to fig. 1, in one exemplary embodiment, an APR system 10 of the present disclosure includes an MPO interface 12, in this case having 4 Tx/Rx sub-fibers. The MPO interface 12 is coupled to Mux WSS 14 and Demux WSS 16, both of which are coupled to amplifiers 18(pre or post) and line amplifiers 22 within module 20, as is conventional. A card CPU or FPGA 24 is provided in the line amplifier 22 and a module CPU or FPGA is provided in the module 20, both operable to implement the functionality of the present disclosure. When the card CPU or FPGA 24 detects a LOS on port 112 (1), the output power of port 112 (1) is compared to an activation threshold. If the activation threshold is exceeded, the HW lines are activated to trigger module 20 to prioritize upcoming APR instructions. In particular, the module 20 is informed by serial communication and, if necessary, HW lines can be used based on timing requirements. These APR instructions are sent to module 24 and indicate on which ports (e.g., port 112 (1)) the APRs are to be applied. Module 24 then applies APR attenuation only to the spectrum that is cross-connected to the affected port (e.g., port 112 (1)). No other ports of the MPO interface 12 (or other MPO interfaces) are affected. It is noted that the power down slew rate can be controlled to mitigate transient effects. For example, the LOS here may be a pulled connector or an optical fiber break, as the purpose is to ensure that the free-space emitted light is at a safe power level.

This method is illustrated in fig. 2. The method 30 begins with a LOS detection 32 on port X. If no LOS is detected, the power or attenuation controller is operating normally and no APR action 34 is taken. If LOS is detected, the power on port X is compared 36 to the activation threshold. If the power on port X has been less than the activation threshold, the power or attenuation controller is operating normally and no APR action 38 is taken. If the power on port X exceeds the activation threshold, the WSS spectrum on port X will be attenuated 40 as part of the APR action.

Fig. 3 shows only such attenuation on port 1. It can be seen that in the example provided, the common input receives comparable WSS spectra relating to the output of ports 1, 2 and 3 before and after the APR. After APR, the WSS spectral output associated with port 1 is attenuated, while the WSS spectral outputs associated with port 2 and port 3 remain unchanged.

Fig. 4 is a schematic diagram illustrating the need for each sub-fiber APR to respond so that other ports are unaffected. Since the APR scheme is only targeted for the WSS spectrum associated with the selected port 50, numerous other ports and channels are unaffected.

It will be recognized that, according to an example, some acts or events of any of the techniques described herein can be performed in a different order, may be added, merged, or omitted entirely (e.g., not all described acts or events are necessary for implementation of the techniques). Further, in some examples, acts or events may be performed concurrently, e.g., through multi-threaded processing, interrupt processing, or multiple processors, rather than sequentially.

In one or more examples, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium and executed by a hardware-based processing unit. Computer-readable media may include computer-readable storage media corresponding to tangible media, such as data storage media, or communication media, including any medium that facilitates transfer of a computer program from one place to another, for example, according to a communication protocol. In this manner, the computer-readable medium may generally correspond to (1) a non-transitory tangible computer-readable storage medium or (2) a communication medium such as a signal or carrier wave. A data storage medium may be any available medium that can be accessed by one or more computers or one or more processors to retrieve instructions, code and/or data structures for implementing the techniques described in this disclosure. The computer program product may include a computer-readable medium.

By way of example, and not limitation, such computer-readable storage media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, flash memory, or any other medium that can store desired program code in the form of instructions or data structures and that can be accessed by a computer. Also, any connection is properly termed a computer-readable medium. For example, if the instructions are transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, Digital Subscriber Line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. However, it should be understood that computer-readable storage media and data storage media do not include connections, carrier waves, signals, or other transitory media, but are directed to non-transitory, tangible storage media. Disk and disc, as used herein, includes Compact Disc (CD), laser disc, optical disc, Digital Versatile Disc (DVD), and blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.

The instructions may be executed by one or more processors, such as one or more Digital Signal Processors (DSPs), general purpose microprocessors, Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs), Complex Programmable Logic Devices (CPLDs), or other equivalent integrated or discrete logic circuitry. Thus, the term "processor" as used herein may refer to any of the foregoing structure or any other structure suitable for implementation of the techniques described herein. In addition, in some aspects, the functionality described herein may be provided in dedicated hardware and/or software modules. Furthermore, the techniques may be fully implemented in one or more circuits or logic elements.

The techniques of this disclosure may be implemented in various devices or apparatuses including Integrated Circuits (ICs) or groups of ICs (e.g., chipsets). Various components, modules, or units are described in this disclosure to emphasize functional aspects of devices configured to perform the disclosed techniques, but do not necessarily require implementation by different hardware units. Rather, as noted above, the various units may be combined in a hardware unit, or provided by a collection of interoperative hardware units, including one or more processors as noted above, together with appropriate software and/or firmware.

Thus, the present disclosure addresses the challenge of laser safety without resorting to additional HM or methods that increase cost and reduce performance. Alternative methods of using WSS to reduce power are: muting the amplifier, which would unnecessarily affect all traffic associated with that dimension (causing collateral damage), or adding light valves (shutters) on all WSS demux ports, which would add thousands of costs and increase ROADM losses, affecting performance. Thus, the present disclosure provides a better solution. Advantageously, the systems and methods provided herein are flexible in the number of active sub-fibers. A response per sub-fiber is provided that uses the incoming LOS to trigger the APR to a level calculated per sub-fiber according to a maximum power limit, e.g., <15dBm, a specific implementation of four sub-fibers per MOP, and given assumptions about photodiode accuracy, etc.

Possible attenuation schemes include fixed attenuation, port-specific fixed attenuation and just enough attenuation. In a fixed attenuation, if an incoming LOS is detected, the spectral attenuation associated with the respective port defaults to a common (settable) value, e.g., about 5dB, regardless of port power. This is simple and fast in response, but may result in unnecessarily large power transients. In port-specific fixed attenuations, the minimum nominal power value per port can be considered. Again, this is simple and responsive, but may still result in unnecessarily large power transients. In just enough attenuation, it is necessary to consider how much higher the output is than the APR activation power and add a large amount of offset to achieve eye-safe levels. This minimizes power transients, but requires more computational complexity. This situation can be mitigated, for example, by preparing an attenuation curve for each port.

Fig. 5 is a flow diagram of an Automatic Power Reduction (APR) process 80 for an optical network module. Process 80 includes, in a multi-fiber interface including one or more ports adapted to be coupled to one or more multi-fiber connectors, detecting, at the card processor, a loss of signal on an input port of the one or more ports and comparing the power of the associated output port to an activation threshold received by the card processor (step 82); and, in the event that a signal loss is detected on the input port and the power of the output port exceeds an activation threshold, triggering, at the module processor, the optical network module to perform an APR procedure and attenuate a spectrum associated with the affected port using a wavelength selective switch coupled to one or more ports (step 84). The card processor and the module processor can be respective functional parts of the same processor.

The process 80 can further include, in the event that a signal loss is detected on the input port but the power of the output port does not exceed the activation threshold, denying triggering, at the module processor, the optical network module to execute the APR procedure and attenuating the spectrum associated with the affected port using a wavelength selective switch coupled to one or more ports. Triggering the optical network module to execute the APR program can include causing the optical network module to execute the APR program at a higher priority than other programs using the communication line. Attenuating the spectrum associated with the affected port using a wavelength selective switch coupled to the one or more ports can include attenuating the spectrum associated with the affected port to a predetermined amount received by the module processor. Attenuating the spectrum associated with the affected port using a wavelength selective switch coupled to one or more ports can include attenuating the spectrum associated with the affected port by a variable amount that depends on a difference between the power of the affected port and an activation threshold received by the module processor.

Although the present disclosure has been illustrated and described herein with reference to preferred embodiments and specific examples thereof, it will be readily apparent to those of ordinary skill in the art that other embodiments and examples may perform similar functions and/or achieve similar results. All such equivalent embodiments and examples are within the spirit and scope of the present disclosure and are therefore contemplated and intended to be covered by the following non-limiting claims for all purposes.

Claims

1. An optical module (10) comprising:

a plurality of ports (12) configured to connect to a multi-fiber cable including transmit and receive optical fibers for the plurality of ports (12);

a detector for each of the plurality of ports, the detector configured to detect loss of signal at a port level; and

a processor (24) configured to perform automatic power reduction only on affected ports (12) of the multi-fiber cable where a loss of signal is detected.

2. The optical network module of claim 1, wherein the multi-fiber cable is an MPO cable.

3. Optical network module (10) according to any of claims 1-2, wherein the detected loss of signal is based on a comparison of the power detected by the detector with a threshold value.

4. Optical network module (10) according to any of claims 1 to 3, wherein the optical module (10) is any of an interconnect module, a dimension module and a multiplexer and demultiplexer module.

5. The optical network module (10) of any one of claims 1-4, wherein a sum of optical power on all optical fibers in the multi-fiber cable exceeds about 21.3 dBm.

6. Optical network module (10) according to any of claims 1 to 5, wherein the automatic power reduction is an attenuation of the spectrum of the affected port caused by a wavelength selective switch (20).

7. Optical network module (10) according to claim 6, wherein the automatic power reduction is prioritized by a hardware line connected to the wavelength selective switch (20).

8. A method, comprising:

receiving a plurality of ports (12) from a multi-fiber cable including transmit and receive optical fibers for the plurality of ports (12);

monitoring the plurality of ports (12) by a plurality of detectors to detect loss of signal at the port level; and

performing automatic power reduction only on affected ports of the multi-fiber cable where a signal loss is detected.

9. The method of claim 8, wherein the multi-fiber cable is an MPO cable.

10. The method of any of claims 8 to 9, wherein the detected loss of signal is based on a comparison of the power detected by the detector to a threshold.

11. The method according to any of claims 8 to 10, wherein the method is performed in an optical module (10), which is any one of an interconnect module, a dimension module and a multiplexer and demultiplexer module.

12. The method of any of claims 8-11, wherein a sum of optical power across all optical fibers in the multi-fiber cable exceeds about 21.3 dBm.

13. The method according to any of claims 8-12, wherein the automatic power reduction is an attenuation of the spectrum of the affected port caused by a wavelength selective switch (20).

14. The method according to claim 13, wherein the automatic power reduction is prioritized by a hardware line connected to the wavelength selective switch (20).

15. A non-transitory computer-readable medium storing computer-executable instructions configured to cause a processor to perform the method of any one of claims 8 to 14.